Why do we want reflow profiles?
Whereas most makers are no less than considerably accustomed to the idea of utilizing a soldering iron to soften solder onto through-hole elements, the world of floor mount is kind of completely different. The method usually entails spreading a skinny layer of solder paste onto the PCB’s uncovered pads, putting the elements, after which reflowing, or melting, the solder paste to make the connections. This final step requires a number of temperature levels to be reached over the course of some minutes which ensures strong bonding and prevents element harm.
From “Reflow Soldering” on Wikipedia
Some present initiatives make the most of repurposed toaster ovens with modified timing circuitry, however Crimson Dynamo needed one thing that could possibly be simply expanded to accommodate all kinds of PCB sizes. His concept was to construct a reflow hotplate that heats boards through direct contact somewhat than sizzling air- all whereas having clever profiles which are utilized over time.
Constructing a heating circuit
To generate sufficient warmth, Crimson went with a pair of 400W, 240V heater plates together with a 10A relay, thermistor (temperature sensor), and metal plate for every. When present is utilized to the plates by means of the closed relays, they can rapidly ramp up their temperature which may then be tempered by means of a microcontroller and thermistor. A cut-out protector was additionally positioned inline to take away energy from the plates within the occasion of thermal runaway.
The controller board
Based mostly on an ESP32 Dev Package V4, the consumer interface board is answerable for presenting choices to the consumer through a 0.96″ OLED display screen and dealing with the choice. As soon as an possibility has been chosen with a rotary encoder, the microcontroller closes the relays after which switches them on or off relying on the present thermistor studying and the goal temperature from the profile because of a PID loop.
Hotplates and enclosures
The excessive voltages and temperatures concerned on this challenge led Crimson so as to add a number of essential security options to his enclosure. First, the hotplates are raised with a collection of standoffs from the bottom, thus stopping them from heating their environment an excessive amount of. Second, all the high-voltage internals are recessed right into a 3D printed plastic enclosure to assist cut back shock dangers. And eventually, the steel construction inside is absolutely grounded as yet one more security measure.
Creating profiles
Crimson started by calibrating his thermocouples with a take a look at mode he programmed which slowly ramps up the voltage being utilized to the hotplates. It then permits the consumer to measure the actual hotplate temperature with a thermometer and report the 2 values. This continues till diploma values starting from 25C all the best way to 200C have been created and related to one another in code. After calibration has completed, thermal profiles, or arrays of temperatures over time, could be loaded into this system and chosen from the display screen.
To learn extra about this good hotplate reflow station, try Crimson Dynamo’s challenge write-up right here.